An associate director in George Mason University's affirmative action office was arrested Tuesday and charged with videotaping a series of sexual encounters he had with a 16-year-old boy.

Ronald J. Sinacore, 55, of the 5400 block of Long Boat Court in Fairfax County, was charged with one count of possessing child pornography and one count of producing child pornography, Fairfax County police said. He is being held without bond at the Fairfax jail.

Sinacore has worked at George Mason since November 1991, when he joined the school's Office of Equity and Diversity Services as an associate director. Among his duties, university officials said, was to counsel employees and managers when issues of sexual and other forms of harassment would arise.

Yesterday, George Mason University spokesman Daniel Walsch said Sinacore has been placed on administrative leave. Walsch had no comment about the investigation except to say, "We're cooperating with the authorities every way we can."

Detectives said they started their investigation Oct. 9 after the victim -- now 20 years old -- reported that Sinacore, a former lover, videotaped them having sex without his knowledge or consent. He told police that he only recently became aware of the videotapes.

According to a search warrant affidavit filed Oct. 20 in Fairfax County Circuit Court, the victim said he met Sinacore four years ago when the youth put personal information about himself on the Internet to meet men. The victim told police he was contacted by Sinacore and they met at the McDonald's in Kings Park Shopping Center in Fairfax County.

Later that day, according to court records, the two started a "casual sexual relationship" that lasted two years. The victim told police they had sex four times: three times at Sinacore's former home on Victoria Road in Fairfax County and once at Sinacore's office at George Mason.

According to the affidavit, the victim ended the relationship with Sinacore when he was 18 years old.

He told police he began to receive instant messages on his computer from Sinacore during the first week of September. While he said he wasn't interested in communicating, he told police, Sinacore followed-up with e-mails, expressing his displeasure. Investigators said Sinacore ended one of his e-mails saying that he had something to show the victim that he'd been holding onto for a while.

Sinacore persuaded the victim to meet at a McDonald's at University Mall in Fairfax, warning at the end of one e-mail, "don't blow me off. . . . it's not a wise thing to do at this point."

At their meeting, according to the affidavit, Sinacore said he had three videotapes of himself and the victim having sex. He said two of the tapes were at home and one was in his office.

On Oct. 15, search warrants were executed on Sinacore's home, vehicle and office at George Mason, where school officials said a computer was confiscated.

Staff writer Maria Glod contributed to this report.